1. Field of the Invention
The present invention relates to a rubber wet master batch containing at least a filler, a dispersing solvent and a rubber latex liquid as raw materials, a process for producing the master batch, a rubber composition, and a pneumatic tire.
2. Description of Related Art
Hitherto, it has been known in the rubber industry that when a rubber composition containing a filler such as carbon black is produced, a rubber wet master batch is used in order to improve the workability of the composition and the dispersibility of the filler. The rubber wet master batch is a material obtained by mixing a filler with a dispersing solvent at a predetermined ratio in advance, dispersing the filler in the dispersing solvent by mechanical force to prepare a filler-containing slurry, mixing the slurry and a rubber latex liquid with each other in a liquid phase state, adding a solidifying agent such as an acid to the mixture to solidify the mixture, and collecting and drying the mixture. In the case of using the rubber wet master batch, a rubber composition is obtained which is better in filler-dispersibility and rubber physical properties, such as workability and reinforcing performance, than in the case of using a rubber dry master batch obtained by mixing a filler and a rubber with each other in a solid phase state. The use of this rubber composition as a raw material makes it possible to produce a rubber product (such as pneumatic tire) that has, for example, a reduced rolling resistance and an excellent fatigue resistance.
As a process for producing a natural rubber wet master batch, Patent Document 1 discloses a process for producing a natural rubber wet master batch that includes the step of mixing a slurry in which a filler such as carbon black is previously dispersed in water with a natural rubber latex, wherein as to the particle size distribution of the filler in the slurry, the 90%-by-volume particle diameter (D90) thereof is adjusted to 30 μm or less. Patent Document 2 discloses a natural-rubber wet-master-batch rubber composition obtained by a producing process of mixing a slurry in which carbon black is previously dispersed in water with a natural rubber latex.    [Patent Document 1] Japanese Unexamined Patent Publication No. 2004-99625    [Patent Document 2] Japanese Unexamined Patent Publication No. 2006-213804